Photographic dye diffusion transfer process

ABSTRACT

FOR THE PRODUCTION OF A COLORED IMAGE BY THE DYE DIFFUSION TRANSFER PRROCESS OF MULTILAYER MATERIAL IS USED WHICH CONTAINS AN IMAGE-RECEIVING LAYER ON A TRANSPARENT SUPPORT, AND A LIGHT-SENSITIVE, DYE-GIVING COMBINATION, AND BETWEEN THEM A LIGHT-IMPERMEABLE BUT DIFFUSION-PERMEABLE LAYER AND STRIPPING MATERIAL TO ENABLE STRIPPING OFF THE IMAGE-RECEIVING LAYER. THE LIGHT-SENSITIVE ELEMENT IS EXPOSED IMAGE-WISE, THEN BROUGHT INTO CONTACT WITH A PRROCESSING COMPOSITION THAT CAUSES IT TO PRODUCE A DYE IMAGE THAT DIFFUSES INTO THE IMAGE-RECEIVING LAYER THEREIN FORMING A TRANSFER IMAGE VISIBLE THROUGH THE TRANSPARENT SUPPORT. WHEN IT IS OBSERVED THAT THE TRANSFER IMAGE IS ACCEPTABLE THE IMAGE-RECEIVING LAYER IS STRIPPED AWAY FROM THE LIGHT-SENSITIVE COMBINATION.

United States Patent US. CI. 96-49 D 6 Claims ABSTRACT OF THE DISCLOSURE For the production of a colored image by the dye diffusion transfer process a multilayer material is used which contains an image-receiving layer on a transparent support, and a light-sensitive, dye-giving combination, and between them a light-impermeable but diffusion-permeable layer and stripping material to enable stripping off the imagereceiving layer. The light-sensitive element is exposed image-wise, then brought into contact with a processing composition that causes it to produce a dye image that diffuses into the image-receiving layer therein forming a transfer image visible through the transparent support. When it is observed that the transfer image is acceptable the image-receiving layer is stripped away from the light-sensitive combination.

The present invention relates to a dye diffusion transfer process preferably carried out in or by means of a photographic camera and to a material for carrying out the process.

Dye diffusion transfer processes which can be carried out in the camera are known in which a photographic material consisting of a support which is impermeable to light and a light-sensitive, dye-giving element (negative) arranged over the support, is exposed imagewise and by means of a suitable mechanical device is then brought into contact with an image receiving layer (positive) on a support, after which a developer paste or activator paste is distributed between the image-receiving layer and the light-sensitive element. After completion of the development process, the negative and positive have to be separated from each other.

An improvement of this relatively complicated process is described in US. Pat. No. 3,415,644. According to that patent the light-sensitive element (negative) and imagereceiving layer (positive) form one inseparable unit and the support for the image-receiving layer is transparent.

After exposure through that transparent support, a vis cous processing mass which contains a pigment is pressed between the light-sensitive element and the image-receiving layer to bring about development. A completed image is obtained within a short time by this method. The negative is not separated from the positive but remains joined to it and is covered by the light impermeable pigment layer which has been pressed in.

A disadvantage of this last-mentioned process is that the image produced is side-reversed. Another disadvantage is that the dyes (this applies also to the process previously described) have to diffuse through the developer paste. This impairs the sharpness of the images.

In another process, a material which contains a light impermeable layer of binder is used between the imagcreceiving layer and the light-sensitive element. Exposure and application of the developer are in this case carried out from above and the image produced is non-sidereversed.

All the known dye diffusion transfer processes have one common disadvantage. This is that it is not possible to exert a controlled influence on the formation of the image by 3,730,718 Patented May 1, 1973 varying the diffusion time and thus prevent the kind of faults in the image which may arise, for example, from faulty exposure or from non-observance of the prescribed temperature during development. Although the last two processes mentioned provide the possibility of observing the image while it is in the process of formation, there is no possibility of adjusting the processes of development and diffusion which are predetermined by the structure of the materials since there is no provision for separation of negative from positive. In the first process mentioned, the negative and positive must remain in contact with each other for an empirically determined length of time before transfer of dye is terminated by the separation. Since the image becomes visible only when positive and negative are separated, no control can be exerted on th formation of the image.

It has now been found that control on the development and diffusion process can be exerted if by means of a suitable combination of layers between the image-receiving layer and the light-sensitive dye-giving element, development of the imagewise exposed light-sensitive element can be effected substantially outside the camera, i.e. in daylight, and the light-sensitive element can be separated from the image-receiving element as soon as the visible image formed in the image-receiving layer has the desired quality.

This invention therefore relates to a process for the production of coloured photographic images by the dye diffusion transfer process, using a material carrying, on a dimensionally stable transparent support and in the following order, an image-receiving layer, a light impermeable binder layer and a light-sensitive, dye-giving element; the photographic images being produced by imagewise exposure of the light-sensitive element from above, development and dye diffusion initiated by the development, and transfer of the diffusing dyes to the image-receiving layer where they produce a colored image visible from underneath. The process is characterized in that after imagewise exposure, the light-sensitive, dye-giving element is brought into contact with an aqueous alkaline processing mass and is covered at the top to exclude light, development thus being started and the dyes, which now become soluble and diffusible in the areas corresponding to the image, being transferred into the image-receiving layer through the light impermeable layer of binder, and in that with the aid of a stripping layer situated between the light-sensitive dye-giving element and the image receiving layer the light-sensitive dye-giving element is separated from the image-receiving layer as soon as willcient transfer of the dyes has taken place.

An object of the present invention is the provision of a material for carrying out the foregoing process.

Yet another object of the invention is the carrying out of the process in or by means of a camera.

The process according to the invention and the material required for carrying out the process will now be described in detail.

The essential constituents of the material are the transparent, dimensionally stable support and the following layers arranged on it in the given sequence: the imagereceiving layer, the light impermeable layer, the stripping layer and the light-sensitive dye-giving element.

If desired, a transparent foil which is impermeable to aqueous alkaline processing masses may be arranged over the light-sensitive element.

This material is exposed imagewise from above, its. from the face remote from the transparent dimensionally stable support, through the uppermost transparent foil if this is present. The light-sensitive element is then brought into contact with an aqueous alkaline processing mass while covered at the top so that no light can enter. Development and imagewise diffusion of dye are initiated in -tl 1e- 1ig-ht:sensitive element by theprocessing mass. The: usion layenpreferably haying..-associated .-with--it a dyediifusible dyes liberated from the dye-giving system in the light-sensitive layer, pass through the stripping layer and .the light; impermeable layer, both permeable to the aqueous processing mass and therefore to the dyes, into the.image-receiving-layer where they are fixed and form acoloredreproduction of theobject which has been 'photographed,.this colored imagebeing visible from underneaththroughwthe transparent, dimensionally stable sup port. v i a Y v Sincethe'undersurface'of the light-sensitive'element is sealed in light-proof manner'by the light impermeable layer of-binder, the material may be removed from the camera as soon as it has also been covered at the top by a-lightproof cover without any risk .of after-exposure of thelight-sensitive element. It is therefore possible to observe .theformation of the image in the image receiving layer, and-as soon .as sufficient dye has been transferred the transfusion process can be terminated by separating the light sensitive element from the image receiving layer. One advantage of the new'process is found to be that colored non-reversed, sharp images of the object being photographed can easily be obtained by a process which can be carried out in or by means of a photographic self processing camera, and the images produced-may be eitherpositive or negative as desired, according to the way, in which the process is carried out. The reason why the images obtained are non-side-reversed is that the photographic material is exposed through a simple photographic optical system (lens) from one side and the image is viewed from the other side of the photographic material. The transparent, dimensionally stable support finally forms over the finished image a transparent, scratch-resistant layer which can be Washed off.

The light-sensitive element generally consists of at least I one, and preferably at least three, light-sensitive emulsion layers each of which has a dye-giving system associated with it. The light-sensitive substance, used in the light-sensitive emulsion layers may be silver halides such as silver chloride, silver bromide or mixtures of these two salts, if desired with a small iodide content of up to 10 mols percent. The silver halides may be dispersedin the usual hydrophilic, water-permeable binders. Thebinder used is preferably gelatine. t-

v The term dye-giving system is understood to mean-"a dye or dye precursor in the form of a compound'which is incorporated in a diffusion-fast form in the light-sensitive element and which, when development is carried out in the presence of the alkaline processing mass, reacts -with the imagewise produced oxidation products of, silver halide developers to split off diifusible dyes which preferably contain acid groups. The dye-giving system'may be chosen frorn various classes of compounds The diffusionfast dye-giving compounds described in German Patent Application P 19 30 215.9 a copy of which is in the file 'of its US. counterpart, now Patent 3,628,952, for example, are particularly suitable for this purpos These compounds split off diffusible dyes in theireaction with 7 7 oxidation products of blackand'whitev developer sub stances and of color-forming developer substancesIAnother useful class of dye-giving compounds ha's' been'described' in German patent specificationYlSIO. 1,095,115,

The compounds mentioned there react with oxidized If multi-colored'images are to be produced, the lightsensitive element preferably contains three silver halide emulsion layers which differ in their sensitivity to the various spectral regions of light, each silver halide emulgiving compound which on.r;levelopment yields a diffusible dye whose color is complementary to the color of light to which the given silver halide emulsion layer is sensitive. For example, the :dyegiving compound associated with the red-sensitized silver h'alide-emulsion layer yields a cyan (blue-greetfl dye, the'dye-giving'compound associated with the'green 'sensitized silver halideemulsioii' tayr yields arnagent'adye' "and'tliefdye-giving compouti ated with the blii e-sens'itive silver halide emu yields a yellow dye. I 1 1 f By associated" is meant that thejdye-giving compound is in colse spatial relationship with its silver halide engul sion. It may be situated in the same layer as the sensitized silver halide emulsion wiIhL whichf it is associated or it may be accommodatedin a layer directly'adjacent to its silver:. halide emulsion layer, i.e. it m ay 'be in the-layer directly above or directly below the silver halide emulsion layer; The lastmentioned arrangements-constitutes a preferred embodiment; According to another embodiment,- the silver halide may, for, example,' be incorporatedtogether with the associated dye-giving system in the form of so-called micro capsules in the layer. In this case, two or more. differently sensitized light-sensitive silver halide emulsions and their associated dye-giving compoundsmay be combined ina single: layer in the form of a so-called mixed grain 'emulsion 'as described, for 1 example, in US.

Pat. 2,698,794... I

Theoxidation products of the developer'pro'd'uced in the process of development of a silver halide emulsion must, of course, react only with the associated dye-giving compound. For this reason, the light-sensitive element generallyeicontains separating interlayers which effectively prevent diffusion of the developer oxidation products. These separating interlayers may contain e..g. suitable substances which react with the developer oxidation products.

In a preferred embodiment,- the light-sensitive element m'ay,for example, have the following structure (from abovedownwa'rds'h y -1 Blue-sensitive silver halide emulsion layer. 1 Layercontaining a compound which yield yellow dye Separatinglayer p Green-sensitized silver halideemulsion layer-H Layer containing .a compound which yields magenta .dye Separating layer.

,kedfsensitized silverhalide; emulsion layer I Layer containing a compound which'yields cyan dye; Y

The sequence in which the silver halide emulsion layers are arranged may, of course, be varied out, in that case the associated layers containing the dye 'givin g compounds must be changed round. accordingly so .tha t the emulsi layers remain associated with their-appropriate dye-giving jcornpoundsl'lf desired, one of the silver halide emulsions,

for example'the blue-sensitive emulsion, may be om;

bined with" its associated dye-giving compound in one layer while the otherdye-giving compounds are arranged in. layersfadiac'eut to 'theirassociate'd emulsion layers.

l A so-calledistr'ipping layer is arrangedunderneatli jtlfe light-sensitive, dye-giving elementj Layers of this. .ty-pe are known. When dry, .they prov ide a firm bond between the layers abovejand, below. them,l e.g. between the lights'ensitive. element and the. image receiying. layer caseof the material according tothe invention, butafter development has taken place ,the stripping layershould provide for easy-separation between the light-sensitive element andthe image-receiving layer. The stripping layer therefore generally consists of; a material. which issoluble in. the aqueous processing-massor at least becomes soft in it -$J b ems ri fo th p m s: a e. f e water-soluble or alkali-soluble derivatives of cellulose'or naturalsubstances similar to cellulose; e. g. hydroxyethyl cellulose, cellulose acetate hydrogeuI-phthalate and sodiurn ,alginate. Water-soluble, non-hardenable synthetic polymers may also be used for this purpose, e.g. polyvinyl alcohol. The stripping layers may also contain lowmolecular weight water-soluble substances as additives, e.g. sugar. When development of the light-sensitive, dyegiving element has been started, diffusion of the aqueous processing mass into the lower layers and therefore also into the stripping layer also begins. Softening of this layer provides the necessary condition which enables the lightsensitive element to be stripped off smoothly at the appropriate moment. The stripping layer must, of course, be permeable to the alkaline processing mass and hence also to the dyes which diffuse out of the light-sensitive element.

Since separation of the photographic material is required to take place between the light-sensitive element and the image-receiving layer, the stripping layer is always arranged between these two parts of the photographic material, but this is not to say that other layers of binders which are permeable to alkali may not also be arranged between the stripping layer and at least one of the two aforesaid parts of the photographic material. It has already been mentioned above that a layer which is impermeable to light should be arranged between the lightsensitive element and the image-receiving layer. The stripping layer may be arranged either above or below the light impervious layer according to how the process is desired to be carried out or, if the light impermeable layer is composed of several partial layers, the stripping layer may be arranged between these. If the process according to the invention is to be used for producing images with an opaque background which are to be viewed by reflected light, at least one light impermeable layer or partial layer should be arranged between the stripping layer and the image-receiving layer. If, on the other hand, it is intended to produce transparencies, no light impermeable layer or partial layer will be situated between the stripping layer and the image-receiving layer.

The light impermeable layer arranged between the lightsensitive, dye-giving element and the image-receiving layer is permeable in the same way to aqueous, alkaline processing masses and hence to the diffusing dyes. It has two main functions. Firstly, it provides an aesthetically pleasing image background to the image obtained in the imagereceiving layer after development. Secondly, it constitutes a light impermeable seal separating the light-sensitive element from the transparent, dimensionally stable support below it. These last mentioned layers which are sufficient- 1y impermeable to light but sufliciently permeable to diffusing dyes may be prepared, for example, from suspensions of inorganic or organic dark pigments, preferably black pigments, for example from suspensions, of carbon black in suitable binders such as gelatin or hydroxyethyl cellulose. In order that the layers may be sufficiently absorbent to incident light to ensure effective exclusion of light from the light-sensitive element during development, which is carried out at least partly in daylight, it is generally suflicient for the layers to have a thickness of 0.5 to 2p and contain in a binder, e.g. in gelatin, to 90% by weight of carbon black (based on the total dry weight). The particle size of the pigments used is comparatively uncritical so long as it is not substantially greater than 0.5a.

The light impermeable layer preferably has not only a black, light-absorbent pigment stratum, but also a light reflecting pigment stratum, preferably a white pigment stratum, arranged below the black pigment stratum. The function of this light reflecting pigment layer is to cover the black layer and provide a white background for the image. Any white pigments are suitable for this purpose so long as their reflecting power is sufiiciently high to provide sufficient reflection in layers which are not too thick. The percentage reflection of incident light is preferably more than 85%. Suitable pigments for the light reflecting layer are, for example, barium sulfate, oxides of zinc, titanium, silicon, aluminium and zirconium, barium stearate, calcium titanate and kaolin. The white pigment preferably used is titanium dioxide. The conditions to be observed as regards the binder, concentration and particle size are the same for the white pigments as for the black pigments. The thickness of the white pigment layer may be varied according to the required whiteness of the background. Thickness of between 1.5 and 6 are preferably used.

It should be noted that the functions of the stripping layer and of the light impermeable layer may be combined in a single intermediate layer arranged between the light-sensitive element and the image-receiving layer. In this case, the light absorbing or light reflecting pigments may, for example, be dispersed in the material of the stripping layer.

The image-receiving layer consists substantially of a layer of binder which contains dye mordants for fixing the diffusing acid dyes.

The mordants used for acid dyes are advantageously longchain quaternary ammonium or phosphonium com pounds or ternary sulfonium compounds, e.g., those described in U.S. Pats. Nos. 3,271,147 and 3,271,148. Certain metal salts and their hydroxides which react with acid dyes to form sparingly soluble compounds may also be used. The mordants are dispersed in one of the usual hydrophilic binders in the receiving layer, e.g. in gelatin, polyvinyl pyrrolidone, completely or partly hydrolysed cellulose esters or the like. Some binders may, of course, themselves function as mordants, e.g. copolymers or polymer mixtures of vinyl alcohol and N-vinyl pyrrolidone, as described for example in German Auslegeschrift No. 1,130,- 284, or those binders which consist of polymers of quaternary bases which contain nitrogen, e.g. polymers of N-methyl-Z-vinyl pyridine as described for example in U.S. Pat. 2,484,430. Other suitable binders which function as mordants are, for example, guanyl hydrazone derivatives of alkylvinylketone polymers, e.g. those described in U.S. Pat. 2,882,156, or guanyl hydrazone de rivatives of acylstyrene polymers as described e.g. in German patent application P 20 09 498.8 published as Offenlegungsschrift 2,009,498. As a rule, however, the last mentioned mordant binders will be used in combination with other binders, e.g. gelatin.

The transparent, dimensionally stable supports for the material according to the invention may be any of the transparent support materials commonly used in photographic practice, e.g. films of cellulose esters, polyethylene terephthalate, polycarbonate or other film-forming polymers.

The light impermeable covering over the top of the light-sensitive, dye-giving element may be obtained by placing a light impermeable covering sheet over the element. The known support materials are suitable for this purpose, e.g. paper alone, or paper laminated with plastics, or foils made of light impermeable film-forming plastics. If development of the material according to the invention is to be carried out outside the camera as already described above, care must be taken in the choice of the material used for the light impervious covering sheet to ensure that it is efliciently lightproof. Dark paper, preferably black paper, may, for example, be used for this purpose. If white paper or transparent foils are used, they are preferably provided with a layer of binder which contains a dark pigment, e.g. carbon black. Supports made of plastics material may advantageously be rendered impervious to light by incorporating dark pigments in them.

If, as already mentioned above, a transparent foil impermeable to the processing mass is placed over the lightsensitive, dye-giving element, the processing mass is pressed between the foil and the light-sensitive element by means of a suitable device and distributed between them. In this case, a lightproof covering is obtained by dispersing a light-absorbent pigment, preferably carbon black, in the processing mass. This then forms a light impervious layer, preferably a black layer, between the transparent foil and light-sensitive element when ithas been pressed between them; 1 I j So long as the lightproof top coveringensure's that light will be effectively excluded, its'natu're is, otherwise of 'minor importance for the quality of the images produced since it is subsequently separated together with the lightsensitive element from the image-receiving layer.

The processing mass is a liquid, viscous o'r pasty alkaline mass which initiates the development of the exposed silver halide. The'developing agents requiredfor developing the silver halide maybe contained in the processingmass or they may be accommodated in one or more layers of the material, for example in one or more layers of .the light-sensitive element or if desired in a separate layer of binder on the lightproof covering'sheet which is placed on the light-sensitive element.

The choice of developing agents depends on the nature of the dye-giving system used. If dye-giving compounds of the type described in German patent specification'N o. 1,095,115 are used, the color developers are preferably of the p-phenylene diamine type, whereas if dye-giving compounds of the type described in Belgian patent specification No. 718,505 and in Dutch patent specification No. 6810479 are used it is generally preferred to use black and whiteidevelopersjThe dye-giving compounds described in German application No. P 19 30 2159 may be developed either with black and white developing agents "or With 'color developing agents.

The following are examples of suitable color 'developers: N,N dimethyl-p-phenylenediamiiie, N,N- diethyl-p-phenylenediamine, monomethyl-p-phenylenediamine, 2 amino 5 diethylaminotoluene, N-butyl-N- w-sulphobutyl-p-phenylenediamine, 2 amino 5 .(N- ethyl N fi methane-sulphonamidoethyl-amino) toluene and the like. Other suitable color developers have been described e.g. in J. Amer. Chem. Soc. 73,3100 to 3125 (1951).

Suitable black and white developers are e.g, hydroquinone and hydroquinone derivatives, pyrocatechol, phenidone and phenidone derivatives, l-(P-T minophenyD- 3-an1inopyrazoline, etc. i

.It has in many cases been found useful to cornbine several developing agents.

' The developing agents are generally required"t(")'be readily ditfusible in an 'alkaline medium so that they can easily reach the exposed silver halide and then, when they have been oxidized, the associated dye-giving system.

On the other hand, in cases Where the developing agents are not (or not exclusively) contained in the processing mass but (also) in the photographic material, they should be as non-ditfusible as possible. It is therefore advantageous to introduce them in a diffusion fast form into i'the layers so that they will not react prematurely with silver halide and thus cause'fogging. Diifusion fast incorporation of the developing agents may be achieved, for example,'by dissolving them in a hydrophobic high- Aschrift No. 1,019,560, in British patent specification Nos.

632,836; 691,815; 783,887; 1,069,061 and 1,114,277 and in U.S. patent specification Nos. 3,243,294 and 3,342,599. Diifusion fast color developers have beenv described in German patent application P 19 31 057.7 published as Offenlegungsschrift 1,931,057. These developers may also advantageously be used in the color-photographic materials according to the invention but they must be used in close spatial relationship with the associated dye-giving compound with which they are-required to react in their oxidized form to liberate the diffusing dyes, and if possible they should even be used in the same layerI'Inthiscase it is also advantageous to use an additional dilfusible auxiliary'de'veloping agent, for example 1 -phenyl-3-' pyra'zolidinonei' l The processing mass may also contain other reagents, for example silver salt solvents, stabilizers, antioxidants or antifogging agents. The'following are 'examplesof substances which may be added to thetpr'ocessing masses to increase the viscosity; cellulose derivatives, for example carboxyalkyl celluloses, hydroxyethyl cellulose, 2-hydrox ypropyl cellulose, starch and polyvinyl alcohol; The processing mass is preferably of high viscosity because it pro motes uniform distribution and complete covering of the surface of the light-sensitive dye-giving element. The aqueous components of the processing mass diifus'e through the light-sensitive element into the stripping layer so that the layer of processing mass, which is situated between the covering sheet (or transparent foil) and the light-sensitive element, becomes depleted of Water and consequently there is a further rise in the viscosity of this layer and the bond between the covering sheet and the light-sensitive element becomes firmer. At the same time, the bond between the light-sensitive element and the image-receiving layer is weakened due to'softening of the stripping layer. The necessary conditions are thus -pro vided to enable separation of the light-sensitive element from the imageqeceiving layer by pulling the covering sheet from the transparent, dimensionally stable support. The alkaline processing mass adjusts the light-sensitive material to a relatively high pH (about 10 to 14) which initiates the development and imagewise difiusion of the dye. It has been found that the dyes and therefore-the images produced are not particularly stable at this high pH. It is therefore advantageous to render'the imagereceiving layer of the material almost neutral or slightly acid when development has been completed. This may be achieved in known manner by including in the material an additional'acid polymer layer which becomes accessible to the alkaline processing mass only gradually in the course of development. An acid polyme'r'layer'is understood to be a layer of binder which contains polymer compounds which have acid goup's, preferably sulfo of carboxyl groups These acid groups react with the cations of the processing mass to form's' alts and th'u s lowerthe pH of the mass. The polymer compounds and hence the acid groups are, of course, incorporated in a diffusion fast form in'the said layer. The acid polymers used are frequently derivatives of cellulose or derivatives of polywith sulfonic acid anhydrides, for example with o-sulfobenzoic acid anhydride, carboxymethyl cellulose, polystyrene sulfonic acid, polyvinyl hydrogen phthalate, polyvinyl acetate hydrogen phthalate, polyacrylic acid, acetals of' polyvinyl alcohol with aldehydes which are substituted with carboxyl or sulfo groups, such as 0-, mor p-b'enz .aldehyde-sulfonic acid or -carboxylic acid, partially esterified. copolymers of ethylene and maleic acid anhydride, partially'esterified copolymers of methylvinyl ether and maleic acid anhydride, and the like.

,The acid polymer layer must containsuflicient acid groups toreduce thepH of theprocessing mass from the original value (it 10' to 14 to such an extent that finally the material is almost neutral. p i

The delay in the lowering of pH is achieved 'in known manner by coating the acid polymer layer with a socalled control layer (timing layer). This control layer is permeable to. alkali and advantageously consists of a polymer which is inert to alkali, for example polyvinyl alcohol. The amount of delay in the lowering of the pH value can be adjusted as desired by suitable choice of the thickness and composition of this control layer.

Combinations of an acid polymer layer with a control layer have been described for example in German patent specification No. 1,285,310. These layer combinations may be present as additional components of the material according to the present invention. In that case they are advantageously arranged between the transparent, dimensionally stable support and the image-receiving layer. These two layers must, of course, be arranged in such a sequence that the alkali in the processing mass must first penetrate the control layer before it can reach the acid polymer layer.

The above mentioned dye-giving systems, both those described in German patent specification No. 1,095,115 or in the above-mentioned German patent application P 19 30 215.9 and those described in Dutch patent specification No. 6810479 or in Belgian patent specification No. 718,505, are negatively operating systems, in other words the diffusing dyes are liberated in areas corresponding to the negative silver image and they produce a negative color image in the image-receiving layer. If the image obtained is required to be a positive, it is necessary either to prepare an intermediate negative copy of the object which is to be p'hotgraphed, this intermediate copy then serving as original for the dye diffusion transfer process, or to use direct positive emulsions in the lightsensitive element or employ suitable reversal processes for the development of the said element.

Direct positive emulsions may for example be those which have a high sensitivity in the interior of the silver halide grains or those which operate by the so-called solarisation principle.

The production of reverse color images by the silver salt diffusion transfer reversal process has been described for example in US. Pat. 2,673,800. In this process, the dye-giving layers of the light-sensitive element contain a dye-giving system and development nuclei for physical development, for example colloidal silver or silver sulfide. The silver halide emulsion layers arranged above the dyegiving layers have a sensitization which is complementary to the color of the associated dye-giving system. In development, silver halide in the unexposed and developed areas of the silver halide emulsion layer is dissolved by the silver salt solvent and deposited physically on the development nuclei in the lower layer by the action of developing agent, and at the same time a difiusing dye is liberated from the corresponding dye-giving system.

According to another process, a reversal efiect is achieved by means of so-called DIR couplers. DIR couplers are color couplers which contain, in the coupling position, a substituent which is split oil in the reaction with the oxidation products of color developing agents and which constitutes a development inhibitor (DIR=development inhibitor releasing). Such DIR couplers have been described, for example, in German Offenlegungsschrift No. 1,422,839. Dye diffusion transfer processes for the production of positive color images with the aid of DIR couplers have been disclosed for example in German patent specification Nos. 1,147,843 and 1,199,- 129. In these processes, the dyegiving layers of the lightsensitive element contain an emulsion which can be developed without exposure to light, e.g. a fogged silver halide emulsion or an emulsion which contains metal salts which can be reduced by developers, and nuclei for the physical development as well as the particular dyegiving system. The DIR coupler is contained in the lightsensitive emulsion layers arranged above this developable emulsion. When development is carried out in the pres ence of a color developing agent, a development-inhibiting compound is split off from the DIR coupler in the exposed areas, and this development-inhibiting compound difiuses down into the lower emulsion layer Where it prevents imagewise development of that emulsion in correspondence with the exposed areas of the light-sensitive emulsion layer.

Another class of compounds which also liberate development-inhibiting substances in the reaction with oxidation products of color developers has been described in German Offenlegungsschrift No. 1,547,640. It has been found that also these compounds may be used in the process according to the present invention instead of the above mentioned DIR couplers for producing positive diifusion images. i

' As already mentioned above, the separating interlayers in the light-sensitive element may contain certain substances which are capable of preventing unwanted diffusion of silver halide, of the development-inhibiting compounds or of developer oxidation products. These substances are chosen according to the particular process employed. Thus in the case of certain embodiments of the process, e.g. when direct positive emulsion are used, it is necessary to ensure that the developer oxidation products formed in the light-sensitive silver halide emulsion layers can diffuse only into their associated dyegiving layer but not into dye-giving layers not associated with them. The undesirable diffusion of developer oxidation products may be prevented, for example, by incorporating in the separating interlayers substances which react with developer oxidation products. In the case of oxidation products of color-developers, for example, it is advantageous to incorporate diffusion fast couplers in the separating interlayers. The undesirable diffusion of silver halide complex salts can be efiectively prevented by adding development nuclei to the separating interlayers. To prevent the undesirable difi'usion of development-inhibiting substances, relatively insensitive silver halide emulsions may be added to the separating interlayers.

Non-difiusing couplers may also advantageously be added to the light-sensitive silver halide emulsion layers themselves in order to trap the developer oxidation products produced in the areas corresponding to the negative silver image and prevent them from diffusing into the associated emulsion layer which is capable of development without exposure to light. This is desired when for example positive images are to be produced by reversal processes form negative emulsions, for example by the silver salt dilfusion process or by means of DIR compounds.

The dye difiusion transfer process according to the present invention may advantageously be carried out in or by means of a suitable self-processing camera. One such camera, for example, contains the light-sensitive multilayered material, consisting of transparent, dimensionally stable support, image-receiving layer, light impermeable layer, stripping layer and light-sensitive element, and the light impermeable "covering sheet, separately from each other. In addition, it must be provided with devices which enable the light-sensitive element to be brought into contact with the processing mass after exposure of the light-sensitive element and at the same time cause the light impermeable covering sheet to be placed on the light-sensitive element so that this element is covered in lightproof manner at the top. A camera of this type is advantageously provided with two squeezing rollers which are mounted side by side in such a way that the light-sensitive material is pulled out between them together with the light impermeable covering sheet and these two parts are bonded together. A camera of the type described in German Offenlegungsschrift 1,597,085 for example is suitable for this purpose.

Distribution of the processing mass over the lightsensitive element of the light-sensitive material may be carried out, for example, in known manner by passing the light-sensitive material over a roller impregnated .With processing mass, with the side carrying the lightsensitive element facing the roller, before it is brought into contact with the light impermeable-covering Sheet. According to another variation, an'air tight'an'dliquidtight cassette filled with processing mass and containing the covering sheet material either in'the form of individual sheets or in the form of a roll is accommodated in the camera so that the covering sheet material is already impregnated with the processing rnass-when "it is removed from the cassette by means of a suitable device and applied to' the light-sensitive element. If the photographic material has a transparent foil over the light-sensitive element, containers which are adapted to be torn open are provided as an additional component of the photographic material. Thesecontainers contain the processing mass and areso'arranged that they are torn open as they pass through the squeezing rollers, whereupon the processing mass is distributed between the foil'and the light-sensitive' element. These openable containers generally consist of a'substantially rectangular, foldable,*air-tight and liquid-tight foil which is folded down its longitudinal axis and the edges of which are thereby brought into contact with each other are bonded together, e.g. by' glueing or welding; A cavity is thus formed which is adaptedto receive the processing mass. This container is so arranged in relation to the material that its "sealed longitudinal edge, which is less firmly sealed than the two transverse edges, 'lies parallel to one edge of the photographic"material" andthat as" soon as an external pressure is'exerted on it, for example-when it passes between the squeezing rollers, thel-ess firmly sealed longitudinal edge is torn open and 'theprocessin'g mass is discharged between the light-sensitive'elemen't and the transparent foil.

Cil

Since the light-sensitive element is protected against unwanted exposure by light impermeable layers' on both sides when it has left the squeezing rollers, the'exposed material may be removed from the camera-as soon'as development has started. The development of the image in the image-receiving layer can be observed i'n"-d'aylight through the transparent, dimensionally stable support, and as soon as the transfer image is seen to' have the required 'quality any further diffusion of dye can be stopped by removing the covering sheettogether with the lightsensitive element from the image-receiving layer.-

Separation of the light-sensitive element'may' advantageously be facilitated by providing flaps overlapping the format of the image at'the sides of the transparent, dimensionally stable support and/or the covering sheet. After separation, theimage-receiving'layer contain's the finished image which can be viewed through the-transparent, dimensionally stable support. To provide additional protection for the image-receiving layer or the lightreflecting layer of binder against mechanical damage, the rear surface may be coated with a layer of lacquer. Alternatively, the finished image may be glued to its final support.

The following example serves to illustrate the invention.

The following layers are applied successively -to a transparent, dimensionally stable support:

(1) A 5% aqueous solution of a copolymer of 2 parts of methylvinyl ether and 3 parts of maleio acid anhydride, molecular weight approximately 50,000, layer thickness (2) A 3% aqueous polyvinyl alcohol solution; layer thickness 3n; I

(3) An aqueous solution containing per litre'25 g. of polyvinyl alcohol (molecular weight approximately 30,000) and 15 g. of polyvinyl pyridine (molecular weight approximately 60,000),'layer thickness 6 (4) A 2.5% aqueous polyvinyl alcohol solution-:containing 1000 g. of TiO per litre, layer thickness 4 t',afl

(5) A 0.5% aqueous gelatin solution containing g. of sodium alginate per litre;-

(6) A silver chloride emulsion containing, per kg;, 15 g. of dye-giving compound No. 1, the formula of, which onipouiid No.

(8)-A silver-iodide emulsion, silver -application 0.2

(9) A'silver chloride emulsioncontaining;per kg. 15 g, of. dye-giving compound No. "2 the formula of. which is shown at the .end of the example, -and.10 ml. of a 2% suspension-of colloidal silver sulfide, silver application vv(l0) A green-sensitized silver iodobromide emulsion containing 12 gcof compound No.4 perkgsilver application 1.2 g./m. 7

(11):A silver iodide emulsion, silver application 0.2

g./m.3; v 1

(12) "A silver chloride emulsion containing, per kg.;, 20 g. of dye-giving compound No. 3 the formula of which is shown at the end of the example, and.10;ml.. of a 2% suspension of colloidal silver sulfide, silver application 1 g./m. 1

(13) An unsensitized silver iodobromide emulsion containing 10 g. of compound No. 4 perkg. silver applica-v tion 1.2- g./m. The material is exposed behind a multicolored original and then covered with a clear foil. A developer paste of the following composition is distributed between-the foil and the light-sensitive material" 15 g. of. N ethyl N-fi hydroxyethyl-p phenylen 10g. of carbon black v 5 g. ,of potassium carbonate l v g. of sodium thiosulfate,' V 20 g. of carboxyrne thyl cellulose madeup v ith wateradjus'tedtb pH"12,5. I

*Since the emulsion-layers ofthe light-sensitive element 'areprotected 'against 'in'cid'ent light-by the layers of car- 'bon ;black,'.the development ofthe :color image can'be observed in daylight. Su-fiicient density ofcolor isobtained after about 3 minutespThefoil is stripped-off to separate. the emulsion layersfrom the image-receiving layenThis completes development. A positive reproduc tion, of the original is obtainedin saturated colors.

I Compound 1 0H 0cm 1 y SO3H horn 1103s" 1 3 Compound 3 In these three formulae Z is What is claimed is:

1. A light-sensitive photographic combination comprising in the following order a transparent support, a diffusionrdye-image-receiving layer, a light-impermeable but dye-difiusion-permeable layer and a light-sensitive element containing at least one silver halide emulsion and a dyegiving compound which provides a difrusible dye upon exposure and development of the silver halide emulsion, said combination also containing stripping material between the light-sensitive element and the image-receiving layer to enable stripping one from the other during development.

2. The combination of claim 1 wherein the light-impermeable binder layer consists of a light-absorbent partial layer and a light-reflecting partial layer and the stripping material is a stripping layer arranged between these two partial layers.

3. The combination of claim, 1 wherein the stripping material is a stripping layer arranged between the light-impermeablelayer and the image-receiving layer.

4. A process for the production of a colored photographic image, which process comprises imagewise exposing the light-sensitive element of the combination of claim 1, then applying to the exposed element a processing mixture that causes the development and the imagewise formation of diffusible dye in the light-sensitive element as well as the diffusion of the dye image through the lightimpermeable binder layer into the image-receiving layer to form therein a colored image visible through the transparent support, viewing the image-receiving layer as the image forms in it while keeping the light-sensitive element protected against light, and when the viewed image has formed sufiiciently stripping the light-sensitive element from the image-receiving layer.

5. The process of claim 4 wherein the light-sensitive element is protected against light by covering it with a light-impermeable covering sheet.

6. The process of claim 4 wherein the light-sensitive element is protected against light by using as a processing mixture one that is impervious to light.

References Cited UNITED STATES PATENTS NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner US. Cl. X.R. 

